The present invention relates to a method for the uniform electrochemical reduction of apertures to micron and submicron dimensions. Further, the present invention relates to spectral filters and methods of making spectral filters for filtering infrared, visible and ultraviolet radiation.
Many techniques exist currently for filtering infrared, visible and ultraviolet radiation. Among these are: mono-chromators (grating or prism types), resonators (for example, Fabry-Perot type), multi-layer dielectric thin films on appropriate substrates, films or bulk materials having appropriate dielectric functions, absorbing colored filters, scatter filters, etc. In practice, all of these techniques are adversely affected, to varying degrees, by environmental factors such as heat, humidity, vibrations, etc.
It is therefore a goal of the present invention to construct metallic meshes with ordered arrays of micro-channels and nano-channels, to characterize their unusual optical and electrical properties, and to exploit their unusual properties in order to detect minute quantities of molecules within the micro- and nano-channels.
Practically speaking, it is a goal of the present invention to construct rugged metallic membranes with ordered arrays of micro- and nano-channels from a variety of metals including some (for example gold and silver) with a known potential for surface enhanced Raman spectroscopy and others (such as copper and platinum) with interesting catalytic properties. It is a further goal of the present invention to produce uniform ordered arrays through the membrane over a region of several square millimeters and with aperture widths from 2 to 6000 nanometers. Additionally, the present invention seeks to use electrical and optical detection techniques to know when and how quickly molecules (including bio-molecules) have moved in and out of the nano-channels. Finally, it is a further goal of the present invention to couple the detection methods to analytical techniques for exploring the potential of such techniques on the nano-scale.
The present invention may be utilized in the following applications: in physical separation and filtering, as in inkjet filters; to limit diffusion which may be important in drug delivery or sensor applications; for regulation and switching of ionic flow and molecular transport; as masks for quantum dot arrays; as a matrix for sensor arrays or lipid bi-layer arrays for bio-analysis; as detection elements in chemical separations and assays, such as xe2x80x9cnano-capillaryxe2x80x9d electrophoresis; in solar selective absorbing surfaces, beam splitters, and optical bandpass filters; and in combinatorial work exploiting the arrays, i.e. put something in each channel. Of course, this list is by no means exhaustive of the potential applications in which the present invention may be employed. Rather, it is meant to be illustrative of the breadth of applications in which the present invention may be used.
Arrays of micro- and nano-channels represent one of the fundamental building blocks of nano-technology. The metallic meshes described herein are strong and flexible enough to be manipulated by hand or with a pair of tweezers. They can be transported without breaking. They may be pressed onto other membranes. They may also be heated without melting. In spite of being fairly rugged, the mesh contains an array of holes with hole-to-hole spacing on the order of microns and a hole diameter that can be closed down to nano-sizes. These meshes represent our interface to the nano-size regime and provide the scaffolding for nano-tech engineering.
The optical properties of grids and meshes become very interesting when the apertures become smaller than the wavelength of probing light. A single aperture (of a non-transparent material) exhibits diminished transmission as the wavelength of probing light becomes larger than the aperture. However, if the apertures are arranged in an ordered array, then long wavelength light can be passed when the wavelength matches the spacing between holes (due to constructive interference). For instance, we purchased commercial 2000 line/inch electro-formed nickel mesh (Buckbee-Mears brand) with 6.5 micrometer square apertures and hole-to-hole spacing of 12.5 micrometers which leaves nominally 26% of the mesh area as open space. Noting that transmission falls from 17 to 14% through the visible, this mesh actually transmits 77% of light around 700 cm xe2x88x921 . Such bandpass phenomena are well known in grating science and are sometimes described as Wood""s anomalies. Most of the mesh or grid devices described in the literature work in the far infrared. They are sometimes called xe2x80x9cinductive gridsxe2x80x9d because their very long wavelength transmission properties can be modeled with an equivalent electrical circuit representation (parallel inductor and capacitor in series with a resistor). The advent of nano-technology or nano-dimensions within the meshes essentially involves pushing the far infrared band pass into the visible. If one wants to study molecules inside or on the surface of a nano-channel, then the constructively-interfering light transmitted by the mesh is particularly useful because only light that has had extensive interaction with the channel is transmitted, i.e. all transmitted photons have passed within less than a half wavelength of everything within the channel. Thus, one can use these membranes to select just the photons containing information about the nano-channel""s contents.
The unusual mesh properties can be exploited to develop sensitive spectroscopic probes of species within the nano-channels. For instance, a metal micro- or nano-channel could be thought of as an optical cavity. Upon illumination of the channel cavity, one might expect the excitation of transverse modes and surface plasmon resonances. Such effects are well known in grating physics and have been exploited to probe proteins embedded in lipid bi-layers attached to thin metal films. We use mesh systems with surface plasmon resonances matched to a probing laser enabling surface enhanced Raman spectra (SERS) to be recorded for species on the surface of the nano-channel. The coupling of SERS with the unusual bandpass properties of metallic mesh arrays, presents an opportunity for a simple, sensitive, chemically specific, and yet remote means to assay the contents of mesh channels.
A method for electrodepositing a uniformly thick coating on a metallic mesh of the present invention comprises the steps of: (1) immersing a metallic mesh in a bath of electrolyte, the metallic mesh comprising at least one aperture having a shape, the electrolyte having an initial concentration and comprising cations and anions in a solvent; and (2) applying an overvoltage to the metallic mesh while immersed in the bath so as to electrodeposit a uniformly thick coating on the metallic mesh thereby forming an initially coated metallic mesh.
It is preferred that the method additionally comprises the step of subjecting the initially coated metallic mesh to a deposition step so as to electrodeposit an additional coating on the initially coated metallic mesh. In this manner the thickness of the coating may be regulated.
While the metallic mesh may be any metallic mesh having suitable properties for the electrodeposition, it is preferred that the metallic mesh comprises a material selected from the group consisting of nickel and composites thereof.
The apertures may be any regular or irregular shapes; however, it is preferred that the apertures have a shape selected from the group consisting of: squares, circles, triangles, rectangles, and polygons. Further, it is preferred that the shape of the aperture is preserved after the uniformly thick coating is electrodeposited. That is to say, the coated aperture has a substantially similar shape to the uncoated aperture.
The uniformly thick coating may be comprised of any material; however, it is preferred that the uniformly thick coating be comprised of a metal selected from the group consisting of copper, platinum, gold, silver, and composites thereof.
The overvoltage applied across the metallic mesh represents the extra energy needed to force the electrochemical cell to proceed at a required rate. It is preferred that the overvoltage be at least 5 volts. It is more preferred that the overvoltage be at least 10 volts.
The present invention includes metallic mesh coated by the aforementioned methods.
In yet another method for electrodepositing a uniformly thick coating on a metallic mesh of the present invention, the method comprising the steps of: (1) providing a metallic mesh having a plurality of apertures having at least one dimension greater than nanometer scale sizes; (2) subjecting the metal mesh to a relatively fast deposition of an electrodeposited material so as to substantially and uniformly coat the metallic mesh with electrodeposited material; and (3) subjecting the product of the relatively fast deposition step to a relatively slow deposition of an electrodeposited material so as to reduce at least one dimension greater than nanometer scale size to a size of nanometer scale.
While the metallic mesh may be constructed of any material suitable for the electrochemical process, it is preferred that the metallic mesh comprises a material selected from the group consisting of nickel and composites thereof.
The uniformly thick coating may comprise any suitable material, however, it is preferred that the uniformly thick coating comprise a metal selected from the group consisting of copper, platinum, gold, silver, and composites thereof.
The apertures may be any regular or irregular shapes; however, it is preferred that the apertures have a shape selected from the group consisting of: squares, circles, triangles, rectangles, and polygons. Further, it is preferred that the shape of the aperture is preserved after the uniformly thick coating is electrodeposited. That is to say, the coated aperture has a substantially similar shape to the uncoated aperture.
The present invention includes metallic mesh having a uniformly thick coating produced in accordance with the aforementioned method.
The present invention includes a coated metallic mesh comprising: (1) a metallic mesh comprising at least one aperture, each aperture having at least one dimension less than about 10 micrometers; and (2) a coating disposed on the metallic mesh, the coating having a thickness, wherein the coating at least partially filling at least one said aperture.
While the metallic mesh may be constructed of any material suitable for the electrochemical process, it is preferred that the metallic mesh comprises a material selected from the group consisting of nickel, and composites thereof.
The uniformly thick coating may comprise any suitable material, however, it is preferred that the uniformly thick coating comprise a metal selected from the group consisting of copper, platinum, gold, silver, and composites thereof. It is preferred that the coating be at least one nanometer thick.
The apertures may be any regular or irregular shapes: however, it is preferred that the apertures have a shape selected from the group consisting of: squares, circles, triangles, rectangles, and polygons. Further, it is preferred that the shape of the aperture is preserved after the uniformly thick coating is electrodeposited. That is to say, the coated aperture has a substantially similar shape to the uncoated aperture.
The present invention also provides a spectral filter comprising: (1) a metallic mesh comprising an array of at least two substantially uniform parallel apertures, each aperture having a shape; (2) a coating disposed on the metallic mesh, the coating having a substantially uniform thickness, wherein the coating partially fills each aperture such that each coated aperture has at least one dimension not greater than about 100 nanometers.
While the metallic mesh may be constructed of any material suitable for the electrochemical process, it is preferred that the metallic mesh comprises a material selected from the group consisting of nickel and composites thereof.
The uniformly thick coating may comprise any suitable material, however, it is preferred that the uniformly thick coating comprise a metal selected from the group consisting of copper, platinum, gold, silver, and composites thereof. It is preferred that the coating be at least one nanometer thick.
The apertures may be any regular or irregular shapes; however, it is preferred that the apertures have a shape selected from the group consisting of: squares, circles, triangles, rectangles, and polygons. Further, it is preferred that the shape of the aperture is preserved after the uniformly thick coating is electrodeposited. That is to say, the coated aperture has a substantially similar shape to the uncoated aperture.
The spectral filter may be a bandpass filter.